CALIBRATING THE BROAD-BAND X-RAY TELESCOPE

This paper describes the calibration of the two solid-state Si(Li) X-r ay detectors and the X-ray telescopes that flew as part of Goddard Spa ce Flight Center's Broad Band X-Ray Telescope (BBXRT) experiment on bo ard the space shuttle Columbia in 1990 December. During the 9 day shut tle mission, BBXRT performed similar to 150 observations of 82 celesti al sources. The content of the archive is summarized here. Although BB XRT had a relatively short life, it stands as a milestone in X-ray ast ronomy as being the first instrument to offer moderate spectral resolu tion over a wide bandpass (0.3-12.0 keV). Among other things, this pap er discusses the effective area calibration of the instrument, the flu x calibration and flux corrections for off-axis observations, the dete ctor background, and optimal background subtraction techniques. The on -axis effective area calibration for the central detector elements was performed using data from the Crab Nebula, while other carefully sele cted targets were used for calibration of the outer detector elements. The remaining systematic uncertainties in the effective area calibrat ion for point sources observed both on and off axis are generally less than 5%-10%. The energy scale is known to better than 0.5% at 6.0 keV for both detectors. The results presented here have an impact on the calibration of other medium resolution X-ray experiments such as the C CDs on board ASCA (Astro-D) as well as the Advanced X-Ray Astrophysics Facility detectors.